The present invention relates to an image forming apparatus such as an electric-photo printing apparatus, a copier, a facsimile, and a multifunctional printing apparatus. In particular, the present invention relates to an image forming apparatus with a toner cartridge detachable thereto for retaining developer, and the toner cartridge provided in the image forming apparatus.
In a conventional image forming apparatus such as an electric-photo printer, toner is retained in a cartridge as developer, and the cartridge is detachably attached to the image forming apparatus, so that toner can be replenished repeatedly. In the image forming apparatus having such a cartridge, it is necessary to detect a remaining amount of toner in the toner cartridge, and to replace the toner cartridge when the remaining amount of toner becomes too small.
In an image forming apparatus disclosed in Patent reference, a rotatable stirring shaft is disposed in a toner cartridge. A rotational timing of the stirring shaft is measured to detect a remaining amount of toner in the toner cartridge.
In such an image forming apparatus, an image forming unit is provided for forming an image. The image forming unit includes a photosensitive drum; a charge unit disposed around the photosensitive drum; a developing unit; and a cleaning unit. In the image forming unit, a toner image is formed on the photosensitive drum. The photosensitive drum has a certain life, and needs to be replaced at the end of the life. Accordingly, the image forming unit is adapted to be detachable relative to a main body of the image forming apparatus, and the toner cartridge is attached to the image forming unit.
Patent Reference: Japanese Patent Publication No. 2003-50505
In the conventional image forming apparatus described above, when the image forming unit is replaced at the end of the life thereof, the toner cartridge is removed from the image forming unit. In this case, if a certain amount of toner is already supplied to the image forming unit from the toner cartridge, the toner in the image forming unit is also discarded, thereby wasting toner.
In view of the problems described above, an object of the present invention is to provide an image forming apparatus, in which it is possible to prevent toner from wasting. Another object of the present invention is to provide a toner cartridge, in which it is possible to prevent toner from wasting.
Further objects and advantages of the invention will be apparent from the following description of the invention.